Eyes on the Radioactive Wind, Scientists in California Study the Fukushima Meltdown

By Veronique Greenwood | August 16, 2011 12:37 pm

fukushimaClean-up teams at Fukushima struggled to control the melting fuel rods.

What’s the News: After the disastrous March 11 earthquake and tsunami in Japan, the world waited, mostly in vain, for details about the events that led to meltdown at the Fukushima Daiichi nuclear plant. Since then, scientists across the Pacific in California have been watching the dials of instruments that detect radioactive molecules, to see what might come across on the winds.

This week, scientists at Scripps published their readings of radioactive sulfur collected in the atmosphere in San Diego after the meltdown. These allowed them to extrapolate backwards to learn roughly how many neutrons were shed by the melting cores as workers desperately doused them in sea water, helping scientists understand the damage undergone by the cores and demonstrating the kind of remote science that may be required to help understand the events that led to meltdown.

How the Heck:

  • The scientists were looking for sulfur-35, a form of sulfur that’s created when chloride ions, plentiful in sea water, are hit by neutrons produced during radioactive decay. One of the researchers told ScienceNOW that she’d read that after underwater nuclear tests in the 1950s and 60s, sulfur-35 levels had skyrocketed, and she’d suspected the same might occur after the Fukushima meltdown.
  • Sure enough, in the weeks after the event, the team saw their sulfur-35 numbers, usually between 180 and 475 atoms per cubic meter of air, leap to 1500. Even this level of sulfur-35 isn’t dangerous; using a computer model, the team estimated that vast majority of radioactive sulfur molecules leaked at Fukushima—about 99.3%–likely dropped into the ocean on the way over or were otherwise dispersed.
  • With their sulfur counts in hand, the team was able to back-calculate how many neutrons would have had to have hit chloride ions in order for that much sulfur to be produced. They estimate that per square meter of reactor space, 400 billions neutrons were released before March 20.

Not So Fast: While such back-calculations are an intriguing way to study the meltdown, an atmospheric scientist interviewed by ScienceNOW points out that the 6,200 miles between Japan and San Diego is a very long way for particles to travel. There must therefore be significant uncertainty in the team’s calculation of how much sulfur-35 was produced in the air above the nuclear plant.

The Future Holds: This study is likely just the harbinger of many more attempts to study the Fukushima meltdown from afar. Be on the lookout for more.

Reference: Priyadarshi, A., Dominguez, G. & Thiemens, M. H. Proc. Natl Acad. Sci. USA http://dx.doi.org/10.1073/pnas.1109449108 (2011).

[via ScienceNOW]

Image: Wikimedia Commons / derek visser

CATEGORIZED UNDER: Physics & Math, Technology, Top Posts
  • Jim

    Why are scientists forced to back calculate from here? Isn’t there any Japanese (or nearby) sharing or divulging of information to either the general public or interested scientists? It’s not like it’s a trade secret – or that people (who are already affected) are going to be any more or less worried based on a number.

    “Well we had a big scary accident, but I can’t really share any more than that.” really?

  • http://discovermagazine.com Iain

    Duh! Jim! Duh! Consumer reaction over an ‘off’ commercial is rabid, how do you think Japanese durable goods manufacturers would suffer if we knew how much radioactive crap was spewed out by Tokyo Electric?
    Ya! Bankruptcies would ensue!

  • Julie

    As a Californian living in Korea, California has got nothing to worry about. It’s got the Pacific Ocean, for god’s sake!

  • John Lerch

    Julie, have you never heard of the Westerlies? As in prevailing winds..

  • dave chamberlin

    Sorry writers of this article, but you are wrong about what the US knew and when they knew it. American naval ships were right off the coast of Fukuashima and knew exactly what the radiation levels were within hours of any large radiation release and they even had drone planes buzzing the sites for further readings. This information wasn’t broadcast because the Japanese public was already so rattled, but they knew. Nobody had to extrapolate backwards except those not privy to this sensitive information. The USA warned its citizens to a larger stay out of zone because they had very accurate knowledge of radiation release from the sites. To imply that readings from San Diego helped to educate anybody about what really happened 6200 miles away is, well, silly.

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